The valves of a hydraulic transmission of the type used in vehicles can be controlled by a microprocessor which includes sensors that sense variables such as road speed, throttle position, engine RPM, and the like. These microprocessors function to provide pulses to pulse width modulated valves as well as power to on/off valves at the appropriate time. These valves can control spool valves for operating clutches in the transmission or they can control the clutches directly. Pulse width modulated valves are normally used when it is desirable to accurately control the pressure of the fluid being supplied through the valve.
Prior art solenoid valves are well known in the art and are able to adequately function in an automotive transmission in both a pulse width modulated mode and an on/off mode. Prior art valves generally have a single piece housing which contains a coil. A pole member extends into the housing through the center of the coil. A ball in included which is movable with the application of power to the coil to open or close fluid passageways to control the flow of fluid. The housing associated with these prior art solenoid valves is generally a machined forging or extrusion. The machining of this forging or extrusion adds a significant cost to the manufacturing costs of the solenoid valve. Accordingly, what is needed is a solenoid valve which incorporates a lower cost method of manufacturing the housing and other components of the valve. The solenoid valve must still meet all the performance characteristics of the valves manufactured with one piece machined housings.
The present invention provides the art with a solenoid valve which has a two piece outer housing which is projection welded together. The cover of the valve is a powdered metal component having an inductioned hardened valve seat. A tubular shaped body is projection welded to the cover to form the two piece outer housing. The internal components of the solenoid are assembled into the body and tabs extending from the body are rolled over to maintain the internal components of the valve within the assembly. The air gap necessary for the operation of the solenoid is adjusted using an externally accessed threaded member which is staked in place to maintain the air gap once the proper gap has been set.
Other advantages and objects of the present invention will become apparent to those skilled in the art from the subsequent detailed description, appended claims and drawings.